The Eltran® method describes a method for the transfer of thin films based on the formation of a fragile or brittle layer in a first substrate, technological steps applied to a surface portion of this substrate such as oxidation, epitaxial growth, making circuits etc., bonding the first embrittled substrate, by this surface portion, to a supporting substrate (by molecular or anode bonding or through adhesives) and splitting provoked at the layer, for example by the application of mechanical stresses. This brittle layer is in principle a porous layer, generally obtained by anodization of the material from a free face; this porous layer is therefore typically situated on the surface at the time of its formation. Inasmuch as this porous layer often needs to be buried at a non-zero depth from the surface, there are known ways of recrystallizing a part of this porous layer whose thickness, taken from the free surface, determines the depth of the residual porous layer. However, most frequently, the initial substrate is complemented by the epitaxial deposit of an additional layer (whence the name of the method, Eltran®, which is derived from “Epitaxial Layer Transfer). Usually, the constituent material of the initial substrate is silicon and the second substrate is electrically insulating, at least on the surface so that, after transfer of the layer of this initial substrate which surmount the porous layer, silicon-on-insulator (SOI) is obtained.
Another method of transfer is known as the “Smart Cut® method”. This is a method for transferring thin films based on the implantation of gas ions, the bonding of the implanted substrate to a supporting substrate and the performance if necessary of technological steps and finally splitting brought about at the implanted zone, for example by heat treatment and/or the application of mechanical stresses.
It will easily be understood that when preparing micro-technological components, i.e. electronic, optical, mechanical and other components with dimensions smaller than one millimeter, or even one micron, it may be necessary to make several transfers so as to carry out technological steps at the different levels of depth needed. However, to prevent any imprecise control over the place at which the splitting takes place, it has appeared to be necessary until now to define steps of elaboration such that there is only one brittle zone, at a given point in time, within a given structure (i.e. a set of substrates or layers assembled by any appropriate means). It will be understood however that such a precaution runs counter to the need for productivity which is a primary concern in the industrial world.